Effect of lattice damage on impurity depth profiles in BF 2+-implanted silicon

Abstract

BF + 2 ions were implanted on n-type Si(100) wafers which were annealed in a rapid thermal annealing furnace and in a conventional furnace. The crystal defects arising from the lattice damage caused by BF + 2 ion implantation and subsequent annealing were investigated using transmission electron microscopy and Rutherford backscattering ion beam channelling. The effects of these defects on the depth profiles of boron and fluorine were analysed by secondary ion mass spectrometry. The depth profiles of both boron and fluorine in the annealed specimens show two peaks and higher peak concentrations are observed for fluorine than in the as-implanted specimen. The two peaks in the fluorine depth profile are observed for all annealed specimens, whereas for boron the two peaks are only observed in specimens that are annealed above 1100 °C. These results indicate that BF + 2 ion implantation produces two types of defect where the boron and fluorine can be gettered and that boron is gettered at a higher temperature due to a lower diffusion coefficient. Transmission electron micrographs reveal only one type of defect, whereas Rutherford backscattering data indicate the possible presence of another type of defect closer to the wafer surface.